The present invention relates generally to heaters and, in particular, a new combustion system for use in a forced-air type heater.
Portable heaters are well known. One type of portable heater for commercial use draws air into the heater and forces the air through a flame. As the air passes through the flame, it is heated and output into a room or other structure which is intended to be heated. This type of portable heater is referred to as a forced-air and/or direct-fired heater. In a direct-fired heater, part of the product of the combustion is output into the room or the structure to be heated.
Direct-fired heaters are fairly distinctive in their appearance since they utilize an elongated cylindrical housing. Within the housing is mounted a means for moving the air (usually at a high velocity) and a combustion system.
The means for moving the air consists of a fan (or a propeller) attached to an electric motor. The motor and fan turn at a constant speed and blow air over the combustion system. The combustion system is designed to burn gas (vapor propane or natural gas). A control circuit releases a pre-determined amount of gas and mixes it with air. The air/gas mixture is ignited at the combustion system and, as long as gas is supplied, the fire stays lit.
Mounted on the outside of the housing are valve(s). The valve(s) are connected between an external gas source and the combustion system by tubing. Normally, the valves are completely closed (i.e., xe2x80x9coffxe2x80x9d) or completely open (i.e., xe2x80x9conxe2x80x9d) and ensure a steady flow of gas to the combustion system. A modulating secondary valve is sometimes utilized.
Air is drawn in by the fan at the inlet or first end of the housing, heated as it passes and mixes with the combustion system and exits through the outlet or second end of the housing.
Although the housing, fan and the electric motor that drives the fan are all fairly typical in such forced-air commercial heaters, the shape and efficiency of the combustion system may be quite different. However, one thing previous burner assemblies in other heaters have in common is that they are not capable of having their input gas flow rate adjusted without affecting safe and efficient combustion. Because of this drawback, most portable direct-fired heaters run at maximum output and are usually designed to produce constant heat while on (e.g., 500,000 British thermal units [Btus] or higher).
In contrast with prior portable commercial heaters, the present invention is an improved heater having a novel combustion system that bums gas more efficientlyxe2x80x94even at reduced gas flow rates. Therefore, the present invention allows the heat output of the heater to be variably controlled. This may be done by replacing the valves with modulating regulators, and connecting the regulators to a new control circuit (e.g., one having a thermostat). Although the present invention is described in connection with a portable heater, it may be utilized by any type of direct-fired heater.